The use of bone screws for fastening implants in an adequately secure manner or for immobilizing joints is known. Depending on the application, positioning between the implant and the bone screw in an angularly rigid manner is sufficient in this connection, in other cases, an angularly variable (polyaxial) arrangement is necessary. To create such a possibility for angular adjustment, it is known to provide a dome-shaped clamping sleeve, which is mounted so as to be tiltable in a corresponding receiving seat in the holding body, between the object that is actually to be held (bone plate or implant) and the bone screw. For fastening, the bone screw is guided through an interior of the tiltable clamping sleeve, the thread of the bone screw engaging not only in the bone located below the holding body but also engaging in a corresponding counter thread on the inner wall of the clamping sleeve by way of its upper region close to the head. When the screw is fastened, not only is it consequently fastened to the bone, but the bone screw is forced onto the clamping sleeve opposite the holding body such that it is fixed in its angular position. In order to achieve the expanding effect necessary for the forcing action, the screw head is realized with oversize relative to the width of the interior. A fastening arrangement of this type is described in US 2005/154392 A1.
One difficulty when handling a fastening arrangement of this type is that the surgeon hardly gets any feeling of when the bone screw has been sufficiently tightened. Precisely for operations at places that are difficult to access or on small and therefore delicate bone parts, it is relatively unreliable to rely just on a feeling for the tightening torque. The use of a torque spanner for this does not create any kind of remedy as the tightening torque can vary considerably depending on the state of the thread (dry or moistened by bodily fluids). In addition, the tightening torque in the case of the afore-described fastening arrangement is further falsified as a result of additional force having to be applied for expanding the clamping sleeve.